Field
The described technology relates to a synchronous motor, and more particularly, to a rotor having a flux filtering function which allows is demagnetization of a permanent magnet installed in the rotor to be suppressed to suppress an efficiency decrease of a motor, and a synchronous motor having the same.
Description of the Related Technology
Generally, motors (or electric motors) are apparatuses which generate a rotational force by converting electric energy into mechanical energy and are widely used for domestic and industrial applications. Such motors are largely classified into alternating current (AC) motors and direct current (DC) motors.
A DC motor, which is a motor driven by DC power and configured to obtain a required output power by changing an input voltage, is used to drive streetcars, elevators, or the like because adjusting a speed thereof is relatively easy. DC motors may be classified into brush DC motors and brushless DC motors. Brushless DC motors do not have a contact portion, such as a brush and a commutator, unlike a brush DC motor, and accordingly a high performance, light, miniaturized, and long lived motor may be realized. In addition, a brushless DC motor has a structure in which coils are wound around a rotor and permanent magnets are embedded in the rotor. Such a brushless DC motor is widely used for various devices based on the development of semiconductor technologies, components, and materials.
An AC motor is driven by an AC power and is the most widely used kind of motor in everyday life. An AC motor basically includes an outer stator and an inner rotor and is a motor in which, when an AC current is supplied to wound coils of the stator, an electromagnetic field is changed by electromagnetic induction, an induction current is generated by a rotating electric field in the rotor, and a rotational force is generated by torque at a rotating shaft positioned in the rotor.
Such AC motors are mainly classified into single-phase motors and three-phase motors and are also classified into induction motors, synchronous motors, and commutator motors based on types of rotors.
A synchronous motor, such as a line start permanent magnet (LSPM) motor (also referred to as a single-phase induction motor), is a kind of motor to which only merits of a single induction motor and a synchronous motor are applied.
Such a synchronous motor is a motor which is started by starting rotation of a rotor due to torque generated by interaction of a secondary current generated by a voltage induced in conductive bars of the rotor and a magnetic flux generated by wound wires of the rotor, and when normally operating, is driven at a speed of a rotation magnetic field of the rotor by synchronizing magnetic fields of permanent magnets installed in the rotor with magnetic fields generated at the stator. That is, when a current is applied to coils of the stator, the rotator rotates due to interaction between a rotating magnetic flux generated due to a structure of the stator and an induction current generated in the conductive bars of the rotor. In addition, when a speed of the rotator reaches a synchronous speed, torque due to the permanent magnets and reluctance torque due to a structure of the rotor are generated and the rotor rotates.
A rotor of such an LSPM motor has a structure including a cylindrical iron core, a plurality of conductive bars inserted into a circumferential edge of the iron core of the rotor, and a plurality of permanent magnets inserted and installed in the conductive bars.
High performance operation is possible by applying a permanent magnet having high performance to an LSPM motor having such a structure, but there is a problem in that demagnetization of the permanent magnet occurs due to an initial operating current applied when initially operating the LSPM motor. That is, the demagnetization of the permanent magnet occurs due to an asynchronous magnetic flux (an AC component) generated at the coils when the LSPM motor initially is operated.
In addition, demagnetization of the permanent magnet also occurs when step out occurs.
There is a problem in that an efficiency of a motor decreases as a demagnetization of a permanent magnet occurs.